Upgrade Ruby

[artur-intech]

@maciej-szlosarczyk You probably want to tune Docker config as well? You mentioned some issue, if I remember correctly...

Closes #137

[maciej-szlosarczyk]

Not tune, but create a custom image as we no longer can use the approved Ruby image for variety of reasons:

• There is no approved image of Ruby 2.5 with Jessie. There's a PR that dates back to February 2018, so it will not happen. Add ruby-2.5.0 based on debian jessie docker-library/ruby#189
• live registry is stuck on Jessie because of EPP and how it is set up with Apache on the same machine.
• Stretch drops postgres-client 9.4, we are stuck with it because upgrading to higher version changes how pg_dump and pg_restore work. We should sooner rather than later move to 9.6 if not for safety then to get UPSERT and parallel queries that came respectively in 9.5 and 9.6.

Anyway, there is extra work involved with this change now and going forward because now we/I have to maintain the docker images even for point releases.

[vohmar]

merge conflicts with master

[artur-intech]

Everything I wanted to merge to master until commit 7fd16c1 (see above) is already in master. No idea why there are some additional commits from Georg are here...

We could just discard this PR, I guess.

[teadur]

@artur-beljajev why not close it then ? the pull request is opened by you ?
As of i dont see the point in bouncing the pull request around i shall close it myself to save everyones time :)